For months, Upton was said to be considering a run to become the Republican nominee for the seat currently held by Democratic U.S. Sen. Debbie Stabenow, who is running for a fourth 6-year term next year.

Republicans had been bullish on their chances to beat Stabenow, with President Donald Trump last year becoming the first Republican presidential nominee to win in Michigan since 1988.

But Upton's decision not to run comes after another widely known potential candidate — the musician Kid Rock — also said he would not run after months of suggesting he might.

Businessman John James, former state Supreme Court Justice Bob Young and historic preservationist Bob Carr are running as Republicans for the Senate. Grosse Pointe businessman Sandy Pensler is also looking at potentially entering the race.

Upton, 64, has been in the U.S. House since 1987 and will be running for his 17th two-year term next year. He is also the former chairman of the House Energy and Commerce Committee.

Contact Todd Spangler at 703-854-8947 or at tspangler@freepress.com. Follow him on Twitter at @tsspangler.